The regions between the hydrophobic core and polar zones of biological membranes (the "hydrogen belts") consist of hydrogen bond acceptors (the C double bond O groups of glycero- and sphinogolipids) and hydrogen bond donors (the OH groups of cholesterol sphingosine, proteins and water). We have postulated lipid-lipid and protein-lipid hydrogen bonding in these belts, and have obtained evidence indicating phospholipid-cholesterol C double bond O---HO interaction. In further studies, we shall seek further confirmation of such hydrogen bonding, and explore the effects that changes in the composition of the hydrogen belts have on the properties and function of membranes. Model lipids are synthesized in which the groups that can partake in hydrogen bonding are abolished (e.g., O-substituted cholesterols, ether and alkyl analogs of phosphatidylcholine and lysophosphatidylcholine). The influence of these structures on membrane permeability, and its energy and entropy of activation, are determined. Monolayer experiments on the lipids, alone and in mixtures, are also performed. Lipid-transfer protein-lipid complexes are investigated in view of the possible importance of hydrogen bonding in lipid transfer. The bonding of stereoisomers of phosphatidylcholine and lysophosphatidylcholine to cholesterol will be studied by nuclear magnetic resonance.